The present invention relates to the production of chlorofluorocarbons and especially chlorofluoroethanes having a hydrogen.
Chlorofluorocarbons are now widely used as aerosol propellants, refrigerants and foaming agents. The use of perhalogenated chlorofluorocarbons (having no hydrogens), especially as aerosol propellants, has been questioned because of the asserted possibility of damage to the earth's ozone layer. Non-perhalogenated chlorofluorocarbons have been suggested as "stratospherically safe" propellants because of the likelihood that they would decompose in the lower atmosphere.
Non-perhalogenated chlorofluorocarbons may be prepared in one or more steps involving replacemtn of hydrogens by chlorine or fluorine. Production of the desired non-perhalogenated chlorofluorocarbon is limited, however, by the coproduction of perhalogenated chlorofluorocarbons as byproducts due to the overhalogenation of the starting material. For example, when 1,1,1-trifluoro-2-chloroethane (fluorocarbon 133a according to the ASHRAE designation) is chlorinated with C1.sub.2 by any method, some overchlorinated byproduct, 1,1,1-trifluoro-2,2,2-trichloroethane (fluorocarbon 113a) is produced. In the absence of a separate use for fluorocarbon 113a, this overchlorination detracts from the overall yield of fluorocarbon 123 based upon both hydrocarbon starting material and halogen reactants. It has now been surprisingly found that the fluorocarbon 113a byproduct can be converted to the fluorocarbon 123 product without the introduction of new reactants into the overall process or significant increases in the halogen waste byproduct stream.
The disproportionation of fluorochlorocarbons is well known in the art. The disproportionation reaction involves an exchange of chlorine and fluorine leading to more highly fluorinated compounds and to compounds of lower fluorine but higher chlorine content. In general, complex mixtures are formed since the disproportionation reaction theoretically can be repeated until compounds having only chlorine atoms and fluorine atoms are left in the mixture. In general, the disproportionation usually does not proceed to this ultimate end.
In contrast to prior art disproportionations, the reaction of the subject invention involves a chlorine-hydrogen exchange in which a perhalogenated hydrocarbon such as fluorocarbon 113a gives up a chlorine atom and receives a hydrogen and a halogenated hydrocarbon such as fluorocarbon 133a gives up a hydrogen and receives a chlorine.